Scanning x-ray system

ABSTRACT

An x-ray apparatus uses an x-ray tube which is pivoted about a pivot axis to provide scanning of an x-ray beam. The pivot axis passes essentially through the center of the focal spot on the target surface of the anode of the tube, is essentially perpendicular to the anode-cathode axis, and is essentially parallel to a film plane defined by the x-ray film. The scanning of the x-ray beam by pivoting the x-ray tube results in improved systems for standard radiography, linear tomography, and large-scale angiography. In standard radiography and large scale angiography systems, moving primary and secondary slots synchronized with the pivoting of the x-ray tube provide efficient removal of secondary radiation. In linear tomography systems, the object and film are moved synchronously with the pivoting of the x-ray tube, and primary and secondary slots which are stationary remove secondary radiation.

This is a continuation of application Ser. No. 071,184, filed Aug. 31,1979 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to radiography. In particular, the presentinvention is an improved scanning x-ray system useful in a wide range ofradiographic systems.

2. Description of the Prior Art

Radiographic systems typically include an x-ray tube which emits x-rays.These x-rays are directed through an object to be studied (such as aportion of the human body) and onto an x-ray film. The x-ray tubetypically includes an anode and a cathode.

When a very high voltage is applied between the anode and cathode, anelectron stream is directed from the cathode along an anode-cathode axisand onto a target portion of the anode. The small area of the targetwhich the electrons strike is called the focal spot, and is the sourceof the x-rays emitted by the tube.

The impact of the electrons at the focal spot generates both x-rays anda significant amount of heat. This heat must be dissipated so that thetarget, and therefore the tube, is not destroyed.

The quality of a radiographic image depends on the size andconfiguration of the focal spot. The smaller the focal spot, the betterthe detail of the image. Ideally the focal spot should be a pointsource. However, since a large spot can tolerate more heat than a smallone, reducing the focal spot to a point source is not feasible withoutreducing the instantaneous heat loading capacity to levels which wouldpreclude use in a clinical radiographic system.

One common technique for reducing the effective size of the focal spotis by using the line focus principle and rotating the anode. The linefocus principle uses a target which is at an angle with respect to aplane perpendicular to the anode-cathode axis. The electron stream isfocused on a narrow rectangle on the target. When the rectangular focalspot is viewed from below the anode, the focal spot is essentiallysquare, and the effective area of the focal spot is only a fraction ofits actual area. The length of the projected focal spot can be decreasedby making the target angle smaller. However, a small target anglecompromises field coverage. For adequate coverage in angiography, x-raytubes having an 11° or 12° target are presently being used. For standardradiography, the target angle has to be larger to allow the coverage ofa 35.9×43.6 centimeter (14×17 inch) radiograph at 1.02 meters (40inches).

Further increases in the capacity of the anode to withstand heat havebeen achieved with rotating anode tubes. In these tubes, the anode isdisk shaped, and has a beveled target area near its end. The cathode isarranged to direct the electron stream against the beveled target areaof the disk, while the disk rotates. The position of the focal spotremains fixed in space while the anode rotates, thereby increasing theeffective area being exposed to the electron beam, while maintaining thefocal spot at a much smaller area than is possible with a stationaryanode.

Since the introduction of the high speed rotating anode x-ray tubes,little progress has been made in significantly increasing instantaneousheat tube loading. As a result, the effective focal spot size forstandard radiographic systems has not been significantly decreased.There is a continuing need for radiographic systems which producesuperior radiographs with high resolution, increased contrast, and lesspatient exposure than in the prior art standard radiographic systems.

Tomography is a special radiographic technique in which a distinct imageof a selected plane through the object is produced, while images ofstructures that lie on opposite sides of the plane are blurred. Thevalue of tomography in clinical practice is well established.

In most presently used tomographic systems the patient remainsstationary, and the x-ray tube and film cassette are moved. In thesetypes of systems, the tube is typically mounted on a long arm, and as itis moved there is unavoidable vibration. As a result, the apparent focalspot size increases due to the vibration, thereby producing geometricunsharpness.

It has been known for many years that tomographs (and in particularlaminographs) can be obtained by moving the object and film cassette andkeeping the radiographic tube stationary. This principle was introducedby Vallebona in "Una modalita di tecnica per la dissociazioneradiografica delle ombre applicate allo studio del cranio", Radiol Med17: 1090-1097, September 1930, and was perfected by Bozetti, whoactually built such an apparatus. See "La realizzazione practica dellastratigrafia", Radiol Med 22: 257-267, 1935. With Bozetti's laminogram,the patient rotated about a craniocaudal axis; and the radiographicplate moved synchronously. This apparatus, however, never became popularbecause structures lying transversely (such as the ribs) could not besufficiently blurred.

Previously, tomography with a linear patient motion was not possiblebecause of the limited field coverage of standard radiographic tubes. Ifthe object and film are moved synchronously, the object would move outof the x-ray beam. This method was suggested by Heckmann in "DieRoentgenperspektive und ihre umwandlung durch eine neueAufnahmetechnik", Fortschr Roentgenstr 60: 140, 139. Heckmann used astationary x-ray tube with the patient and cassette moving in oppositedirections. With this technique, only a very small area of the bodycould be examined, and therefore the method was impractical.

Another form of tomography which has presently found use ispantomography, which is described by Pantero in "A new tomographicmethod for radiographing curved outer surfaces", Acta Radiol 32: 177,1949. In this system, the patient and a curved x-ray film rotate inopposite directions to yield a true laminogram. This type oflaminography is useful only for the examination of the jaw.

Conventional tomography, therefore, has the shortcoming of poorresolution due to vibration of the x-ray tube, poor contrast due to ahigh fog level, and restriction to cuts parallel to the patient table.It is desirable to improve further the quality and diagnostic yield oftomography, and to provide means by which tomograms can be made oforgans difficult to image because they do not lie in a plane parallel tothe patient table.

Still another radiographic technique is angiography--the study of bloodvessels. In some cases it is necessary to study the arteries from theabdomen of a patient all the way down to his toes. This large fieldcoverage has necessitated special angiographic systems. In many casesthe x-ray tube in an angiographic system must be mounted a largedistance from the patient table in order to achieve the desired fieldcoverage. This has required an extremely high ceiling of the room withinwhich the angiographic system is located. In some cases, an entireradiology department must be specially designed to accommodate a roomwith an extremely high ceiling in order to house the angiographicsystem.

There is a continuing need for an angiographic system which provides thenecessary wide field coverage and yet can be housed in a conventionalroom, rather than requiring a room with an extremely high ceiling.

SUMMARY OF THE INVENTION

The present invention is an improved x-ray apparatus. In the presentinvention pivoting means pivot an x-ray tube about a pivot axis toprovide scanning of the x-ray beam produced by the x-ray tube. The pivotaxis passes essentially through the center of the focal spot in thex-ray tube, is essentially perpendicular to the anode-cathode axis, andis essentially parallel to the film plane defined by the x-ray film. Thex-ray apparatus of the present invention yields significantly improvedresults in a wide range of radiographic applications, including standardradiology, linear tomography, and large field angiography.

The present invention preferably also includes primary slot meanspositioned between the x-ray tube and the object, and secondary slotmeans positioned between the object and the x-ray film plane. Means areprovided for causing relative motion of the primary and secondary slotmeans with respect to the object and the x-ray film. This relativemotion is synchronized with the pivoting of the x-ray tube.

In standard radiographic systems and angiographic systems utilizing thepresent invention, the primary and secondary slot means are preferablydriven in synchronism with the pivoting of the x-ray tube. In lineartomographic systems utilizing the present invention, the object and thefilm are driven in synchronism with the pivoting of the x-ray tube,while the primary and secondary slot means remain stationary.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view illustrating the pivoting tube scanningx-ray apparatus of the present invention.

FIG. 2 is a partial sectional view of an x-ray tube illustrating thepivot point utilized in the present invention.

FIG. 3 is a graph showing focal spot size as a function of applied gridvoltage.

FIG. 4 is a graph showing maximum exposure times in seconds for variouspeak voltages for a x-ray tube biased at -200 volts grid bias.

FIG. 5 is a front elevational view of a preferred embodiment of astandard radiography system utilized in the present invention.

FIG. 6 is a top view showing the x-ray tube of the apparatus of FIG. 5.

FIG. 7 is a view along line 7--7 of FIG. 5 showing the x-ray tube, theprimary slot device, and the pivot arm which drives the tube and theprimary slot device.

FIG. 8 is a top view of the secondary slot device.

FIG. 9 is a section along line 9--9 of FIG. 8 showing the secondaryslots and drive mechanism.

FIG. 10 is a section along line 10--10 of FIG. 8.

FIG. 11 is a section along line 11--11 of FIG. 10.

FIGS. 12A and 12B illustrate operation of the secondary slot device.

FIG. 13 is a front elevation of a large scale angiography systemutilizing the pivotal x-ray scanning of the present invention.

FIG. 14 is a sectional view along line 14--14 of FIG. 13.

FIG. 15 is a diagrammatic front elevation illustrating the operation ofthe apparatus of FIG. 13.

FIG. 16 is a top view illustrating the operation of the secondary slotand its relation to the film in the system of FIGS. 13 and 15.

FIGS. 17 and 18 are diagrammatic views illustrating the operation of thepresent invention to produce linear tomographs.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 show the basic concept of the scanning x-ray system of thepresent invention. As shown in FIG. 1, x-ray tube 10 provides a narrowbeam of x-rays 12. Tube 10 is pivoted about pivot axis 14, so that beam12 is scanned across object 16 and x-ray sensitive film 18 to produce anx-ray exposure of x-ray film 18.

FIG. 2 shows a preferred embodiment of tube 10. As shown in FIG. 2, tube10 is a rotating anode type x-ray tube having a cathode 20 and arotating anode 22. Anode 22 is a beveled tungsten disk having a targetsurface 24 oriented at an angle with respect to anode-cathode axis 26.Electrons from cathode 20 are directed onto target surface 24 at a focalspot 28, and x-rays 12 are emitted from focal spot 28. As shown in FIG.2, aperture stop 30 selects only those rays emanating from the mostshallow portion of target 24 (i.e. furthest from cathode 20).

In the present invention, tube 10 is pivoted about pivot axis 14 andprovides scanning of x-ray beam 12. Pivot axis 14 is perpendicular toanode-cathode axis 26, is parallel to the plane of film 18, and passesexactly through the center of focal spot 28. As a result, focal spot 28remains effectively stationary and no loss of sharpness occurs from thepivotal movement of the tube.

One important advantage of the present invention is that it permits thefocal spot size to be reduced without significantly compromising thetube heat loading. First, because the beam 12 is scanned, the fieldcoverage of beam 12 need not be the entire field required to be covered.As a result, the effective size of the focal spot can be reduced bybiasing the grid electrode (not shown in FIG. 2) of the x-ray tube 10.

Second, because the required field coverage of beam 12 is smaller due toscanning, the target angle of target 24 with respect to anode-cathodeaxis 26 can be reduced significantly in comparison to the normal targetangle required. This also reduces the effective size of focal spot 28,thereby increasing resolution.

Third, aperture stop 30 may be used to select only a narrow portion ofthe x-ray beam 12 emanating from the most shallow portion of the target(i.e. the portion furthest from cathode 20). This eliminates the opticaldensity gradient (heel effect) which is normally present in standardradiography.

Fourth, due to scanning of the beam 12 by pivoting tube 10, theresolution gradient normally present along the anode-cathode axis inprior art systems is eliminated.

In one successful embodiment of the present invention a standard, gridcontrolled General Electric Maxi-ray 100 tube with a 6.5° target and 0.3and 0.6 mm nominal focal spot sizes was used. The target heat loadingcapacity was rated as 20 kW and 60 kW for the 0.3 and 0.6 mm nominalfocal spot sizes, respectively. This type of x-ray tube permitted anegative bias voltage varying from 0 to 400 volts to be applied to thegrid. The generator for driving the x-ray tube was a three-phase, twelvepulse unit.

The x-ray tube 10 was mounted on a stand which permitted rotation oftube 10 about pivot axis 14 passing exactly through the center of thefocal spot 28. Pivot axis 14 was perpendicular to the anode-cathode axis26 and parallel to the film plane (as is illustrated schematically inFIGS. 1 and 2). The manufacturer of the x-ray tube indicated theapproximate location of focal spot 28 on the outside of the tubehousing. Finer adjustments were accomplished by using magnifiedradiographs of fine wires and a paralactic correction technique. By thismethod, tube 10 was mounted so that pivot axis 14 passed exactly throughthe center of the focal spot 28.

The dimensions of the smaller (0.3 mm nominal) focal spot in theunbiased mode were measured with a star resolution pattern using theSpiegler and Breckenridge method and were found to be 0.5×0.5 mm. See,Spiegler P., Breckenridge W.C.: "Imaging of Focal Spots by Means of theStar Test Pattern", Radiology 102: 679-684, March 1972. When the gridwas biased, the pin hole images obtained showed dramatic reduction inthe width of the focal spot. No significant further shrinkage of thefocal spot was obtained with negative grid biases of more than 200volts. The measurement of the focal spot with 200 volts negative gridbias showed a 0.15 mm width and only a slight change in its length, from0.40 to 0.36 mm. The change in dimensions of the focal spot with varyingtube bias is shown in FIG. 3. Both pin hole camera measurements andSiemens star measurements are shown.

The striking reduction of the width of the focal spot was alsodemonstrated by taking a magnification view of the star pattern.Resolution increased dramatically, but in only one dimension. However,if the star pattern was radiographed toward the anode side of the x-raytube, both dimensions of the calculated focal spot size were reduced to0.2 mm. By using aperture stop 30 (as shown in FIG. 2) and thereby usingonly the portion of the x-ray beam toward the anode side while maskingout the remainder of the beam, a field of only 5 cm (2 inches) long iscovered, but the width of the beam was not altered. A field coverage of43.6×5 cm (17×2 inches), of course, is not useful in the prior artstandard radiographic systems. In the present invention, however, anarea of 35.9×43.6 centimeter (14×17 inches) or larger can easily becovered by this narrow beam (i.e. 17×2 inches) by pivoting tube 10 aboutpivot axis 14 to scan beam 12 across the area.

As discussed previously, the quality of a radiographic image dependslargely on the size and configuration of the focal spot. This isparticularly true for a magnified image. Although ideally the focal spotshould be a point source, this is not feasible without reducing theinstantaneous heat load capacity to levels precluding clinical use. Thisapproach was recently chosen by one of the microfocus tubemanufacturers; but it allows a tube rating of only 2 mA at 100 kV,seriously limiting its clinical application. The length of the projectedfocal spot can be decreased by making the target angle small because ofthe line focus principle, but a small target angle compromises fieldcoverage. In the prior art radiographic systems, x-ray tubes of 11° or12° target angle are used to provide adequate field coverage. Forstandard radiography, the target angle required has been even larger toallow for coverage of a 35.9×43.6 centimeter (14×17 inch) radiograph at1.02 meter (40 inch).

The undesirable configuration of the 0.3 millimeter focal spot of theunbiased General Electric Maxi-ray 100 tube was reduced to a uniform 0.1millimeter focal spot by a negative grid voltage. Although theapplication of the negative grid bias voltage decreased the tube outputsomewhat, a clinically acceptable tube rating was still maintained, asshown in FIG. 4, which is a tube rating chart of the effective 100micron focal spot using a -200 volt grid bias. It is apparent from FIG.4 that with a negative bias of -200 volts, an x-ray exposure of 2seconds at 100 kV and 100 mA is feasible.

In the prior art, standard radiographs have not only a considerablegradient of resolution along the anode-cathode axis, but there is alsoan optical density gradient (heel effect). By pivoting x-ray tube 10about pivot axis 14, (as illustrated in FIG. 1 and 2) the resolution anddensity gradients disappear. By biasing the 0.6 mm focal spot andpivoting the x-ray tube, a 0.3×0.3 mm effective focal spot was obtained,thus allowing high quality standard magnification radiography with amagnification factor up to 1.8 to 2. By applying the bias to the 0.3 mmnominal focal spot, it was possible to produce a microfocal spot with anexcellent tube rating which lends itself very well for radiography ofgreater than 2× magnification.

The scanning x-ray system of the present invention can be used toadvantage in a wide variety of radiographic systems. For example,increased resolution and elimination of optical density and resolutiongradients can be achieved in standard radiographic systems and inradiographic systems having magnification of up to three or four timesutilizing the present invention. In addition, the pivoted scanning oftube 10 in the present invention can be used to great advantage in largefield angiography, and in linear tomography.

The Radiography Apparatus of FIGS. 5-12B

In FIGS. 5-12B, a preferred embodiment of the present invention used instandard and magnification radiography is shown. The apparatus of FIGS.5-12B utilizes the pivoted scanning x-ray tube as shown in FIGS. 1 and2.

In FIG. 5, which is a front elevational view of the apparatus, x-raytube 10 is pivotally connected to downwardly extending arms 40, which inturn are connected to mounting bracket 42. Tube 10 is pivotallyconnected to arms 40 so that it may be pivoted about pivot axis 14. Asdescribed in conjunction with FIGS. 1 and 2, the pivot axis 14 isperpendicular to the anode-cathode axis, is parallel to the plane of thefilm, and passes exactly through the center of the focal spot.

In the apparatus of FIG. 5, a table formed by legs 44 and table top 46provide support for an object (not shown). The x-ray film 18 is locatedin film tray 48. In the apparatus of FIG. 5, legs 44 of the object tableare of a telescoping type, so that table top 46 may be raised andlowered with respect to film 18. The position of table top 46, andtherefore the object, with respect to film 18 determines themagnification of the x-ray image recorded on x-ray film 18.

The apparatus of FIG. 5 includes primary slot device 50 and secondaryslot device 52. Primary slot device 50 is positioned below collimator 54and x-ray tube 10 and is positioned above table top 46. Secondary slotdevice 52 is positioned between table top 46 and film 18.

The purpose of primary and secondary slot devices 50 and 52 is toeliminate secondary radiation which would otherwise fog x-ray film 18.Both primary slot device 50 and secondary slot device 52 include aplurality of slots which are aligned with respect to the primary raysfrom x-ray tube 10. As tube 10 is pivoted about pivot axis 14, the slotsof slot devices 50 and 52 move with respect to the object and x-ray film18 so that the slots themselves will be blurred and will not appear onthe x-ray film 18.

In the apparatus shown in FIG. 5, secondary slot device 52 is supportedby legs 56. Film tray 48 is connected to the bottom of secondary slotdevice 52.

In the embodiment of the present invention shown in FIGS. 5-12B, primaryand secondary slot devices 50 and 52 are driven synchronously with thepivoting of x-ray tube 10. Drive means 58 (shown in FIG. 5) includesgear reduction motor 60, clutch/brake 62, and drive chain 64. Pivot arm66 is linked to drive chain 64 at its lower end and is connected tox-ray tube 10 at its upper end. As drive chain 64 is driven, pivot arm66 follows drive chain 64 at its lower end, thereby causing x-ray tube10 to rotate about pivot axis 14. In addition, pivot arm 66 is linked toboth primary slot device 50 and secondary slot device 52. For thatreason, the pivoting of x-ray tube 10 is synchronized with the movementof primary slot device 50 and secondary slot device 52. As illustratedin FIG. 5 pivot arm 66 preferably moves within a triangular shapedhousing 68.

FIGS. 6 and 7 show the connection of pivot arm 66 and x-ray tube 10.Shafts 70 and 72 are connected to tube 10 and extend through arms 40 topermit tube 10 to be rotated about pivot axis 14. Pivot arm 66 isattached to shaft 70 so that as pivot arm 66 moves, tube 10 is rotatedabout pivot axis 14. This causes scanning of the x-ray beam produced bytube 10.

Primary slot device 50 and secondary slot device 52 are generallysimilar in construction, and include a plurality of spaced elongatedslots through which the primary rays from x-ray tube 10 may pass.Secondary rays such as those produced by scattering of radiation fromthe object are blocked. Primary slot device 50 is smaller than secondaryslot device 52 because it is positioned more closely to x-ray tube 10.In the preferred embodiment shown in FIGS. 5-12B, devices 50 and 52 areof the same general construction, but of different scale.

In order to provide maximum absorption of secondary radition whilepermitting the primary radiation to pass, the slots of slot devices 50and 52 have a significant dimension along the direction of travel of theprimary rays. In the preferred embodiment of the present invention shownin FIGS. 5-12B, the slot devices 50 and 52 are driven along parallelpaths in a linear direction by their linkage to drive chain 64 and pivotarm 66. The slots, however, must remain aligned with the primary raysfrom tube 10 at all positions along their linear travel. In thepreferred embodiments of the present invention, the slots themselves arepivoted about pivot axis 14 so as to maintain the correct angularorientation. In addition, the widths of the slots are maintainedconstant at all positions along their linear travel.

FIGS. 8-12B show secondary slot device 52 which provides linear movementof an array of slots, while pivoting the slots about pivot axis 14 andmaintaining width of the slots constant. Primary slot device 50 is ofsimilar construction, but, as described previously, of a smaller scale.A detailed discussion of secondary slot device 52, therefore, also isapplicable to the construction of primary slot device 50.

As shown in FIG. 8, drive chain 64 is driven by motor 60 through chain74 and clutch/brake 62. The upper and lower runs of chain 64 areoriented parallel to the plane of x-ray film 18 and to the planes of thelinear motion of primary and secondary slot devices 50 and 52.

Secondary slot device 52 includes housing 76 containing four parallelguide rods 78a-78d. Guide rods 78a and 78b lie in an upper plane, whileguide rods 78c and 78d lie in a lower plane directly below rods 78a and78b, respectively. All four guide rods 78a-78d have their axialdirection parallel to the direction of travel of driven chain 64.

Slidably mounted on guide rods 78a and 78b are upper transverse members80a and 80b, respectively. Similarly, lower transverse members 80c and80d are slidably mounted on guide rods 78c and 78d. Transverse members80a-80d extend in a direction perpendicular and transverse to guide rods78a-78d.

Upper longitudinal members 82a and 82b extend parallel to guide rods 78aand 78b, and are attached at their one ends to upper transverse member80a and at their opposite ends to upper transverse member 80b.Similarly, lower longitudinal members 82c and 82d are connected betweenlower transverse members 80c and 80d.

Pivotally connected between upper longitudinal members 82a and 82b andbetween lower longitudinal members 82c and 82d are a plurality of metalmembers 84 and 86 which define slots 88 through which x-ray radiationmay pass. As best shown in FIG. 9 and in FIGS. 12A and 12B, each metalmember 84 has a generally C-shaped cross-section with a generallyvertical portion 84a, a top flange 84b, and a bottom flange 84c.Similarly, each member 86 has a generally C-shaped cross-section whichis a mirror image of member 84. Metal member 86 has a generally verticalportion 86a, a top flange 86b, and a bottom flange 86c. In addition,each member 84 has an inverted L-shaped flap 90 attached to verticalportion 84a with the generally horizontal portion of flap 90 extendingin the same direction as top and bottom flanges 84b and 84c. Similarly,each member 86 has an L-shaped flap 92 attached to vertical portion 86awith its outward portion extending generally parallel to and extendingin the same direction as flanges 86b and 86c.

Top flanges 84b and 86b, bottom flanges 84c and 86c, and flaps 90 and 92cooperate to block x-ray radiation from passing through secondary slotdevice 52 except through slots 88. This effectively blocks any secondaryradiation from the object, since the slots 88 are oriented to receiveonly the primary rays.

The width of slots 88 are maintained constant by spacers 94a and 94b,which are located at opposite ends of each slot 88. Spacers 94 maintainthe width of slots 88 constant throughout the movement and pivoting ofslots 88. Metal members 84 and 86 are attached to and move with spacers94.

The upper ends of spacers 94a are pivotally connected to upperlongitudinal member 82a by pivot pins 96a. Similarly, the upper ends ofspacers 94b are pivotally connected to upper longitudinal member 82b bypivot pins 96b. Pivot pins 96a and 96b all lie in a common plane whichis parallel to guide rods 78a and 78b. Each pivot pin 96a has acorresponding pivot pin 96b which is connected to longitudinal member82b, and each pair of pivot pins define a common pivot axis. At thelower ends of spacers 94a and 94b are slots 98a and 98b, respectively.Slots 98a and 98b ride on pins 100a and 100b which are attached to lowerlongitudinal members 82c and 82d, respectively. Pins 100a and 100b alllie in a common plane which is parallel to guide rod 78c and 78d. Eachpin 100a and its corresponding pin 100b defines a common axis.

The secondary slot device 52 illustrated in the Figures is driven fromchain 64 so that the slots 88 move linearlly and are pivoted about pivotaxis 14 when x-ray tube 10 is rotated about pivot axis 14. In thismanner, slots 88 are always oriented to receive primary rays from tube10. The connection between drive chain 64 and the moving secondary slots88 is provided through linkage arm 102, which is pivotally connected bypin 104 to chain 64. The upper end of linkage member 102 is connected toupper longitudinal drive member 104a, which extends between the ends oftransverse members 80a and 80b. The pivotal connection of linkage member102 with member 106a is by means of pivot pin 108a. Lower longitudinaldrive member 106b extends between the ends of cross members 80c and 80d.Linkage member 102 has a slot 110 which engages pin 108b, which isfixedly connected to member 106b. Pins 104, 108a and 108b are allaligned in a common plane with pivot axis 14.

As chain 64 moves, the lower end of linkage member 102 moves. As aresult, members 106a and 106b, and the remainder of the moving slotapparatus moves along guide rails 78a-78d. Because pin 108b ispositioned more closely to chain 64 than is pivot pin 108a, the lowermembers 82c and 82d, and therefore the lower ends of spacers 94a and 94bwill experience a larger longitudinal movement than the upper members82a and 82b and the upper ends of spacers 94a and 94b. The resultingmotion transmitted from chain 64 to the moving slot device by linkagearm 102 causes each slot to be translated in a direction parallel toguide rods 78a-78d and also to pivot about pivot axis 14.

The synchronized motion of slots with the pivoting of tube 10 isprovided by pivot arm 66 which is fixedly connected near its lower endto linkage member 102 by spacer block 112 and pins 114a and 114b (whichride in slot 110).

The synchronized motion of the slots within primary slot device 50 isprovided by linkage arm 116 which is connected by spacer block 118 andpins 120a and 120b to pivot bar 66. The opposite end of linkage member116 is connected to the moving slot device 50 in a similar manner to theconnection of linkage member 102 with secondary slot device 52.

FIGS. 12A and 12B illustrate the operation of the moving slot devices ofthe present invention in providing a linear translation of the slots 88while pivoting each slot 88 about pivot axis 14 and maintaining thewidth of each slot 88 constant. In FIG. 12A, the slots 88 are shown inan essentially vertical orientation, while in FIG. 12B the same slotshave been translated to the left and have been pivoted about pivot axis14.

In order to maintain the width of slots 88 constant, the spacing betweenadjacent slots is varied. The present invention provides this variablespacing between adjacent slots because members 84 and 86 are notconnected to one another. As a result, the spacing between members 84and 86 can vary except where spacer blocks 94a and 94b positively definetheir spacing. Flanges 84b and 84c and cooperating flanges 86b and 86c,together with L-shaped members 90 and 92 block all radiation betweenadjacent slots 88 regardless of the orientation of the slots. Theflanges and L-shaped members block radiation without requiringconnection of adjacent members 84 and 86.

In operation, pivot arm 66 is originally positioned in its rightmostposition as illustrated in FIG. 5. The person of whom the x-ray is to betaken lies horizontally on table top 46 and the operator of the x-rayequipment initiates an x-ray exposure cycle by actuating the switch (notshown).

When the exposure cycle begins, x-rays are emitted from x-ray tube 10 topass through the object (i.e. the patient's body) and expose x-ray film18 within film tray 48. The x-rays are in a narrow beam of, for example,17 inches×2 inches, as has been described previously. Chain 64 begins tobe driven so that the lower end of pivot arm 66 moves leftward. Themovement of chain 64 causes tube 10 to be rotated about pivot axis 14and the slots within primary and secondary slot devices 50 and 52 tomove synchronously with the rotation of tube 10. When the lower end ofpivot arm 66 reaches the opposite (left) end of its travel, the x-rayexposure cycle is terminated.

The apparatus shown in FIGS. 5-12B provides superior radiographs withhigh resolution, increased contrast, and less patient exposure than hasbeen possible in conventional radiography. Both standard radiographicimages and radiography with magnification has been successfully achievedutilzing the apparatus shown in the Figures.

The Large-Scale Angiography Apparatus of FIGS. 13-16.

The present invention, which utilizes the scanning of an x-ray beam bypivoting the x-ray tube about a pivot axis passing through the center ofthe focal spot, also provides significant advantages when utilized inangiography--the study of blood vessels.

In some cases it is desirable to provide angiographic images of thearteries all the way from the abdomen down to the toes of the patient.In the past, large-scale angiography apparatus has required an extremelyhigh ceiling to mount the x-ray tube a large distance from the patienttable in order to provide the necessary field coverage of the x-rays.

The apparatus of the present invention illustrated in FIGS. 13-16provides large-scale angiography with an apparatus which is smaller andmore effective than the prior art devices. FIGS. 13 and 14 illustratethe structure of the apparatus of the preferred embodiments, while FIGS.15 and 16 schematically illustrate the system of FIGS. 13 and 14.

As shown in the Figures, x-ray tube 10 is again mounted to rotate aboutpivot axis 14. Tube 10 is supported near the top of frame 140 bymounting bracket 142. Tube 10 is fixedly connected to bracket 142. Frame140 has a pair of cross members 144 (one of which is partially brokenaway in FIG. 13) having holes which rotatably receive a pair of shafts146. Mounting bracket 142 has a pair of upstanding arms 148 to whichshafts 146 are connected. As bracket 142 is rotated about the pivot axis14 defined by shafts 146, tube 10 is also rotated. Adjustment screws 150permit adjustment of the position of tube 10 with respect to bracket 142so that the pivot axis 14 is precisely positioned to pass through thecenter of the focal spot of tube 10. Adjustment screws 150 permitadjustment both in a horizontal and a vertical direction.

The patient is supported on object table 154. A second table 156 islocated below object table 154 and supports a film pack 158 containingthe x-ray film 18. As shown in FIG. 13, the length of the film pack maybe essentially the entire length of the patient lying on the objecttable. As a result, an extremely long angiographic image may be producedwith the apparatus. Film vacuum hold 162 applies a vacuum between filmpack 158 and table 156 to hold film pack 158 and film 18 securely inposition during an exposure cycle.

As in the standard radiography apparatus shown in FIGS. 5-12B, thelarge-scale angiography apparatus utilizes moving primary and secondaryslots. The apparatus of FIGS. 13-16, however, utilizes only a singleprimary slot 164 and a single secondary slot 166.

Primary slot 164 is defined by a pair of metal plates 168a and 168b.Plates 168a and 168b are attached to guide blocks 170, which ride on apair of guide rods 172.

Similarly, secondary slot 166 is defined by a pair of plates 174a and174b, which are connected to guide blocks 174, which in turn ride on apair of guide rods 176.

Primary slot 164, secondary slot 166, and x-ray tube 10 are drivensynchronously by motor 178 through chain drive 180, linkage arm 182,bracket 184, linkage 186, and pivot arm 188. Linkage arm 182 isconnected to drive chain 180 by pivot pin 190, and is attached at itsupper end to the secondary slot device. Bracket 184 and linkage 186connect guide blocks 174 of the secondary slot device with pivot arm188. The primary slot device is similarly connected to pivot bar 188,and bracket 142 is connected to pivot arm 188 so that movement of pivotarm 188 causes tube 10 to rotate about pivot axis 14.

As chain drive 180 moves, secondary slot 166 is driven from right toleft in FIGS. 13 and 15 and pivot arm 188 pivots from right to leftabout pivot axis 14. This causes primary slot 164 to move from left toright in a linear motion, and causes x-ray tube 10 to rotate about pivotaxis 14.

In operation, x-ray beam 12 is scanned in a narrow beam defined by slots164 and 166 from one end of x-ray film 160 to its opposite end. Becausethe movement of x-ray tube 10 is a rotational movement about pivot axis14 rather than a lateral translation, problems of vibration areeliminated. An extremely wide field coverage is provided by scanning thenarrow x-ray beam 12 rather than requiring the beam to cover the entirefield of interest simultaneously.

In some applications, the rate of scanning of the x-ray beam can becoordinated with the rate of travel of dye through the patient's body.In this manner, the x-ray beam can effectively be scanned so as tofollow the travel of the dye down the person's body.

As in the case of the standard radiography apparatus describedpreviously, the large-scale angiography apparatus of FIGS. 13-16provides improved resolution, increased contrast, and less patientexposure than the prior art apparatus. In addition, the apparatus of thepresent invention is significantly smaller than the prior art apparatusproviding the same field coverage. In particular, the present apparatuscan fit in a conventional size room, and does not require an abnormallyhigh ceiling. As a result, it can find application in areas where aspecial room with a high ceiling is not feasible or desirable.

The Linear Tomography Apparatus of FIGS. 17 and 18

As described in the previous embodiments, the scanning of an x-ray beamby pivoting the x-ray tube about a pivot axis passing through the centerof the focal spot provides significant improvement in standardradiography and in large-scale angiography. FIGS. 17 and 18 show anotherembodiment of the present invention, and illustrate the advantageous useof the pivoted scanning x-ray tube of the present invention in lineartomography.

In the embodiment illustrated schematically in FIG. 17, x-ray tube 10 isagain pivoted about pivot axis 14, which passes through the center ofthe focal spot and is parallel to the plane of the x-ray film 18. Asx-ray tube 10 is rotated about pivot axis 14, object 16 and x-ray film18 are moved linearlly parallel to one another in synchronous fashion.

In FIG. 17, x-ray tube 10 is shown in two positions. In the firstposition, tube 10, x-ray beam 12, object 16 and film 18 are all shown inphantom. In the second position, tube 10 has been rotated about axis 14and is shown in solid lines, as are beam 12, object 16 and film 18.

At the same time that tube 10 is being rotated about axis 14 to thesecond positon, object 16 and film 18 are being translated to the leftas shown in FIG. 17. The translation of object 16 and film 18 isdesignated by arrows 200 and 202, respectively.

In the present invention, as shown in FIG. 17, points lying within focalplane 204 (which is within object 16) are projected at the same locationon film 18 throughout the scan of x-ray beam 12 and the movement ofobject 16 and film 18. Points lying outside focal plane 204 will beblurred, so that true tomograms are produced.

This is illustrated in FIG. 17 by points A, O and B which lie in plane204 and by point C which lies above plane 204. At the beginning of thescan, when object 16 and film 18 are at their first (right) position inFIG. 17, the projection of point C on film 18 is located between theprojections of points O and A.

As tube 10 is rotated about pivot axis 14, object 16 and film 18 aretranslated to the left as illustrated by arrows 200 and 202 until theyreach the second position illustrated in FIG. 15. Throughout themovement of object 16 and film 18, points B, O and A of plane 204continue to be projected on the same positions on film 18. This isillustrated by the second position in which the projection of points B,O and A on film 18 are designated as B', O', and A'. As shown,projections B and B', projections O and O', and projections A and A'correspond.

In the case of point C, however, which falls outside of plane 204, itsprojection changes as tube 10 is rotated and object 16 and film 18 aretranslated. In the second position, the projection (C') of point C onfilm 18 is now to the left of the projection of point O-O'. The changingpositions of the projection of point C (and all other points lying outof the plane 204), causes these points to be blurred, while theprojections of points lying in plane 204 reinforce one another toproduce a linear tomogram of superior diagnostic quality.

The movement of object 16 and film 18 in synchronism with the rotationof tube 10 is preferably provided by a pivot arm which is driven by anappropriate drive such as a drive chain in a manner generally similar tothe embodiments which have been previously discussed. The pivot arm (notshown in FIG. 15) is linked to tube 10, to the table on which object 16rests, and to the tray containing film 18.

FIG. 18 illustrates another preferred embodiment of the lineartomography apparatus of the present invention. The apparatusschematically illustrated in FIG. 18 is generally similar to theapparatus of FIG. 17 with two important modifications. First, a set ofprimary slots 206 is positioned between tube 10 and object 16, and asecond set of secondary slots 208 is positioned between object 16 andfilm 18. Primary and secondary slots 206 and 208 provide efficientabsorption of secondary radiation without increasing the radiation doseto the patient. Since object 16 and film 18 both move as tube 10 isrotated, primary slots 206 and secondary slots 208 may remain stationaryand will be efficiently blurred.

Second, film 18 may be tilted at an angle with respect to horizontal asshown in FIG. 18. As a result, it is possible for the apparatus of FIG.18 to obtain tomographic cuts parallel to the organ of interest even ifthat organ does not lie parallel to the table top. In standardlaminography only cuts parallel to the table top are possible. Thepresent invention, therefore, allows greater interpretation andreduction of the number of cuts in order to study an organ which isdifficult to image using classical methods, such as the kidney or commonduct. These organs are not parallel to the table top and consequently,in the prior art techniques the upper and lower poles of the kidneycannot be seen simultaneously on the same tomogram. The additional cutsrequired in the prior art to study an organ increases the exposure tothe patient, which is clearly undesirable. Using the present invention,the organ may be visualized tomographically along its long axis bytilting the plane of film 18 and therefore the number of tomographiccuts and the amount of exposure of x-rays to the patient can besignificantly decreased.

The use of slots 206 and 208 in the system of FIG. 18 reduces scatteredradiation much more effectively than the prior art radiographic grids.Residual radiographic fog is decreased from about 35 percent (with agrid) to approximately 8 percent. The dose to the patient, therefore, ismuch lower as compared with standard radiographic grids.

The scanning beam linear tomography illustrated in FIGS. 17 and 18 hasmany important advantages over the prior art linear tomography. First,true linear tomograms can be performed along the long axis of the body,as in standard tomography. Second, vibration of x-ray tube 10 iseliminated since it is merely rotated about pivot axis 14, rather thanbeing translated in position. Third, a 100 micron focal spot x-ray tubemay be used, as described in conjunction with the other embodiments ofthe present invention, thereby resulting in improved resolution anddefinition. Fourth, a stationary primary and secondary slot system asshown in FIG. 18 markedly reduces scatter, thereby resulting in betterimage contrast. Fifth, radiographic cuts parallel to the long axis oforgans are feasible by tilting film 18, thereby reducing the number ofnecessary tomographic layers. Sixth, the patient's exposure dose isreduced since no Bucky is used. Seventh, a book film cassette no longerdegrades diagnostic information and further reduces radiation to thepatient.

Conclusion

The x-ray apparatus of the present invention provides significantadvantages for a wide range of radiographic applications. The scanningpivoted x-ray tube utilized in the present invention has beensuccessfully used in standard radiography, magnification radiography,linear tomography, and large-scale angiography. The significantadvantages of the present invention can also be applied to a wide rangeof other radiographic applications.

Although the present invention has been described with reference topreferred embodiments, persons skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. An x-ray apparatus for producing x-ray images ofan object, the x-ray apparatus comprising:x-ray sensitive meanspositioned on one side of the object for receiving x-rays which havepassed through the object, the x-ray sensitive means defining a fieldover which x-rays are received, the field having a first dimension in afirst direction and a second dimension in a second direction; x-raysource means positioned on an opposite side of the object from the x-raysensitive means for providing a narrow x-ray beam having a firstdimension at the field defined by the x-ray sensitive means which is atleast equal to the first dimension of the field having a seconddimension at the field defined by the x-ray sensitive means which isless than the second dimension of the field and less than the firstdimension of the narrow beam, the x-ray source means including an x-raytube in which an electron stream from a cathode is directed along ananode-cathode axis to strike a focal spot on a target surface of ananode to produce x-rays, the target surface being inclined with respectto a first plane which (1) is perpendicular to the anode-cathode axisand (2) passes through the center of the focal spot; and pivoting meansfor pivoting the x-ray source means about a pivot axis to cause thenarrow x-ray beam to be scanned in the second direction across the fielddefined by the x-ray sensitive means to cover the second dimension ofthe field, wherein the pivot axis (1) passes exactly through the centerof the focal spot, (2) is perpendicular to the anode-cathode axis, (3)lies in the first plane, (4) is parallel to the field defined by thex-ray sensitive means, and (5) is parallel to the first direction sothat as the x-ray source means is pivoted by the pivoting means, thecenter of the focal spot remains stationary.
 2. The x-ray apparatus ofclaim 1 wherein the x-ray source means further comprises:means mountedto and movable with the x-ray tube as the x-ray tube is pivoted forlimiting the x-rays emitted from the x-ray tube to the narrow beam whichis located, with respect to the first plane, on a side of the firstplane which is furthest from the cathode.
 3. The x-ray apparatus ofclaim 1 and further comprising:primary slot means positioned between thetube and the object; secondary slot means positioned between the objectand the x-ray sensitive means; means for causing relative motion,synchronized with pivoting of the x-ray tube, of the primary andsecondary slot means with respect to the object and the x-ray sensitivemeans.
 4. The invention of claim 3 wherein the means for causingrelative motion comprises:first drive means for driving the primary slotmeans in synchronism with the pivoting of the x-ray tube; and seconddrive means for driving the secondary slot means in synchronism with thepivoting of the x-ray tube.
 5. The invention of claim 1 wherein thepivoting means comprises:pivot arm means having an upper end connectedto the x-ray tube; and drive means connected to a lower end of the pivotarm means for driving the lower end to pivot the pivot arms means andthe x-ray tube about the pivot axis.
 6. The invention of claim 5 andfurther comprising:primary slot means positioned between the tube andthe object; means connecting the primary slot means and the pivot armmeans to drive the primary slot means in synchronism with pivoting ofthe x-ray tube; secondary slot means positioned between the object andthe x-ray sensitive means; and means connecting the pivot arm means andthe secondary slot means to drive the secondary means in synchronismwith pivoting of the x-ray tube.
 7. The apparatus of claim 6 wherein thedrive means comprises a chain drive.
 8. The invention of claim 7 whereinthe means connecting the pivot arm means and the secondary slot meanscomprises:linkage means linking the chain drive and the secondary slotmeans; and connecting means connecting the secondary slot means and thepivot arm.
 9. An x-ray apparatus for producing x-ray images of anobject, the apparatus comprising:a source of x-rays which includes anx-ray tube in which an electron stream from a cathode is directed alongan anode-cathode axis to strike a focal spot on a target surface of ananode to produce x-rays, the target surface being inclined with respectto a plane which is perpendicular to the anode-cathode axis and whichpasses through the focal point; x-ray sensitive means positioned so thatthe object is interposed between the source of x-rays and the x-raysensitive means; pivoting means for pivoting the x-ray tube about apivot axis which passes exactly through the center of the focal spot, isessentially perpendicular to the anode-cathode axis, and is essentiallyparallel to a plane defined by the x-ray sensitive means; primary slotmeans positioned between the tube and the object; secondary slot meanspositioned between the object and the x-ray sensitive means; first drivemeans for driving the primary slot means in synchronism with thepivoting of the x-ray tube; and second drive means for driving thesecondary slot means in synchronism with the pivoting of the x-ray tube;wherein the primary slot means comprises:movable primary slot supportmeans driven by the first drive means; a plurality of primary slotssupported by the primary slot support means to pivot about pivot axiswhile the primary slot support means is driven by the first drive means;means for maintaining widths of the primary slots substantially constantwhile the primary support means is driven by the first drive means; andmeans for varying spacing between adjacent primary slots while theprimary slot support means is driven by the first drive means.
 10. Theinvention of claim 9 wherein the primary slot support means is moved bythe first drive means essentially parallel to the plane defined by thex-ray sensitive means.
 11. An x-ray apparatus for producing x-ray imagesof an object, the apparatus comprising:a source of x-rays which includesan x-ray tube in which an electron stream from a cathode is directedalong an anode-cathode axis to strike a focal spot on a target surfaceof an anode to produce x-rays, the target surface being inclined withrespect to a plane which is perpendicular to the anode-cathode axis andwhich passes through the focal point; x-ray sensitive means positionedso that the object is interposed between the source of x-ray means andthe x-ray sensitive means; pivoting means for pivoting the x-ray tubeabout a pivot axis which passes exactly through the center of the focalspot, is essentially perpendicular to the anode-cathode axis, and isessentially parallel to a plane defined by the x-ray sensitive means;primary slot means positioned between the tube and the object; secondaryslot means positioned between the object and the x-ray sensitive means;first drive means for driving the primary slot means in synchronism withthe pivoting of the x-ray tube; and second drive means for driving thesecondary slot means in synchronism with the pivoting of the x-ray tube;wherein the secondary slot means comprises:movable secondary slotsupport means driven by the second drive means; a plurality of secondaryslots supported by the secondary slot support means to privot about thepivot axis while the secondary slot support means is driven by thesecond drive means; means for maintaining widths of the secondary slotssubstantially constant while the secondary support means is driven bythe second drive means; and means for varying spacing between adjacentsecondary slots while the secondary slot support means is driven by thesecond drive means.
 12. The invention of claim 11 wherein the secondaryslot support means is moved by the second drive means essentiallyparallel to the plane defined by the x-ray sensitive means.
 13. An x-rayapparatus for producing x-ray images of an object, the apparatuscomprising:a source of x-rays which includes an x-ray tube in which anelectron stream from a cathode is directed along an anode-cathode axisto strike a focal spot on a target surface of an anode to producex-rays, the target surface being inclined with respect to a plane whichis perpendicular to the anode-cathode axis and which passes through thefocal point; x-ray sensitive means positioned so that the object isinterposed between the source of x-rays and the x-ray sensitive means;pivoting means for pivoting the x-ray tube about a pivot axis whichpasses exactly through the center of the focal spot, and is essentiallyperpendicular to the anode-cathode axis, and is essentially parallel toa plane defined by the x-ray sensitive means, wherein the pivoting meanscomprises:pivot arm means having an upper end fixedly connected to anx-ray tube; and drive means connected to a lower end of the pivot armmeans for driving the lower end to pivot simulatenously the pivot armmeans and the x-ray tube about the pivot axis; primary slot meanspositioned between the tube and the object; means connecting the primaryslot means and the pivot arm means to drive the primary slot means insynchronism with pivoting of the x-ray tube; secondary slot meanspositioned between the object and the x-ray sensitive means; meansconnecting the pivot arm means and the secondary slot means for drivingthe secondary slot means in synchronism with pivoting of the x-ray tube;and wherein the primary and secondary slot means each comprise:a pair ofgenerally parallel upper guide rods and a pair of generally parallellower guide rods; an upper slot support means movable on the upper guiderods and a lower slot support means movable on the lower guide rods;slot defining members spaced from one another to define a plurality ofgenerally parallel slots through which primary radiation from the x-raytube may pass, wherein the slot defining members comprise a plurality ofmembers oriented essentially parallel to a path of primary radiationfrom the x-ray tube; a plurality of spacers which are pivotallyconnected to the upper slot support means proximate their upper ends andare slidably connected to the lower slot support means proximate theirlower ends, the spacers defining a width of the slot.
 14. The inventionof claim 13 wherein each spacer has a longitudinal slot at its lower endwhich engages a pin connected to the lower slot support means forslidably connecting the spacer to the lower slot support means.
 15. Theinvention of claim 14 wherein the upper and lower slot support means areconnected to the pivot arm means.
 16. The invention of claim 13 andfurther comprising:radiation blocking means connected to the slotdefining members for blocking radiation from passing between adjacentslots defined by the slot defining members.
 17. The invention of claim16 wherein the radiation blocking means comprise flanges at upper andlower ends of the slot defining members.
 18. The invention of claim 17wherein the radiation blocking means further comprise metal flap meansattached to the slot defining members to block radiation passing betweenadjacent slots.